Natural gas liquid fractionation plant waste heat conversion to simultaneous power, cooling and potable water using modified goswami cycle and new modified multi-effect-distillation system

ABSTRACT

Certain aspects of natural gas liquid fractionation plant waste heat conversion to simultaneous power, cooling and potable water using modified Goswami Cycle and new modified MED system can be implemented as a system. In an example implementation, the system includes a waste heat recovery heat exchanger network coupled to multiple heat sources of a Natural Gas Liquid (NGL) fractionation plant, the heat exchanger network configured to transfer at least a portion of heat generated at the multiple heat sources to a first buffer fluid and a second buffer fluid flowed through the first heat exchanger network. The system includes a first sub-system configured to generate power and sub-ambient cooling capacity, the first sub-system thermally coupled to the waste heat recovery heat exchanger. The system includes a second sub-system configured to generate potable water from brackish water, the second sub-system thermally coupled to the waste heat recovery heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of priority to U.S. Application Ser.No. 62/542,687 entitled “Utilizing Waste Heat Recovered From Natural GasLiquid Fractionation Plants,” which was filed on Aug. 8, 2017, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to operating industrial facilities, for example,a natural gas liquid fractionation plant or other industrial facilitiesthat include operating plants that generate heat, for example, a naturalgas liquid fractionation plant.

BACKGROUND

Natural gas liquid (NGL) processes are chemical engineering processesand other facilities used in petroleum refineries to transform naturalgas into products, for example, liquefied petroleum gas (LPG), gasoline,kerosene, jet fuel, diesel oils, fuel oils, and such products. NGLfacilities are large industrial complexes that involve many differentprocessing units and auxiliary facilities, for example, utility units,storage tanks, and such auxiliary facilities. Each refinery can have itsown unique arrangement and combination of refining processes determined,for example, by the refinery location, desired products, economicconsiderations, or such factors. The NGL processes that are implementedto transform the natural gas into the products such as those listedearlier can generate heat, which may not be reused, and byproducts, forexample, greenhouse gases (GHG), which may pollute the atmosphere. It isbelieved that the world's environment has been negatively affected byglobal warming caused, in part, due to the release of GHG into theatmosphere.

SUMMARY

This specification describes technologies relating to cooling capacitygeneration, power generation or potable water production from waste heatin a natural gas liquid (NGL) fractionation plant.

The present disclosure includes one or more of the following units ofmeasure with their corresponding abbreviations, as shown in Table 1:

TABLE 1 Unit of Measure Abbreviation Degrees Celsius ° C. Megawatts MWOne million MM British thermal unit Btu Hour h Pounds per square inch(pressure) psi Kilogram (mass) Kg Second S Cubic meters per day m³/dayFahrenheit F.

Certain aspects of the subject matter described here can be implementedas a system. In an example implementation, the system includes a wasteheat recovery heat exchanger network coupled to multiple heat sources ofa Natural Gas Liquid (NGL) fractionation plant, the heat exchangernetwork configured to transfer at least a portion of heat generated atthe multiple heat sources to a first buffer fluid and a second bufferfluid flowed through the first heat exchanger network. The systemincludes a first sub-system configured to generate power and sub-ambientcooling capacity, the first sub-system thermally coupled to the wasteheat recovery heat exchanger. The system includes a second sub-systemconfigured to generate potable water from brackish water, the secondsub-system thermally coupled to the waste heat recovery heat exchanger.

In an aspect combinable with the example implementation, the systemincludes a control system connected to the heat exchanger network andthe first sub-system or the heat exchanger network and the secondsub-system or the heat exchanger network, the first sub-system and thesecond sub-system, the control system configured to flow fluids betweenthe NGL fractionation plant, the heat exchanger network one or both ofthe first sub-system or the second sub-system.

In another aspect combinable with any of the previous aspects, thefluids include one or more of a NGL fractionation plant stream or abuffer fluid.

In another aspect combinable with any of the previous aspects, themultiple heat sources include a first multiple sub-units of the NGLfractionation plant, the first multiple sub-units including a propanedehydration section, a de-propanizer section, a butane de-hydratorsection, and a de-butanizer section, second multiple sub-units of theNGL fractionation plant, the second multiple sub-units including ade-pentanizer section, an Amine-Di-Iso-Propanol (ADIP) regenerationsection, a natural gas de-colorizing section, a propane vapor recoverysection and a propane product refrigeration section and third multiplesub-units of the NGL fractionation a propane product sub-coolingsection, a butane product refrigeration section, an ethane productionsection and a Reid Vapor Pressure (RVP) control section.

In another aspect combinable with any of the previous aspects, the heatexchanger network includes multiple heat exchangers.

In another aspect combinable with any of the previous aspects, themultiple heat exchangers includes a first subset including one or moreof the multiple heat exchangers thermally coupled to the first multiplesub-units of the NGL fractionation plant.

In another aspect combinable with any of the previous aspects, the firstsubset includes a first heat exchanger thermally coupled to the propanedehydration section and configured to heat a first buffer stream usingheat carried by a propane de-hydration outlet stream from the propanede-hydration section, a third heat exchanger thermally coupled to thebutane de-hydrator section and configured to heat a second buffer streamusing heat carried by a butane de-hydrator outlet stream, a fifth heatexchanger thermally coupled to the de-butanizer section and configuredto heat a third buffer stream using heat carried by a de-butanizeroverhead outlet stream from the de-butanizer section, and a sixth heatexchanger thermally coupled to the de-butanizer section and configuredto heat a fourth buffer stream using heat carried by a de-butanizerbottoms outlet stream from the de-butanizer section.

In another aspect combinable with any of the previous aspects, thesecond subset includes a seventh heat exchanger thermally coupled to thede-pentanizer section and configured to heat a fifth buffer stream usingheat carried by a de-pentanizer overhead outlet stream from thede-pentanizer section, an eighth heat exchanger thermally coupled to theADIP regeneration section and configured to heat a sixth buffer streamusing heat carried by an ADIP regeneration section overhead outletstream, a ninth heat exchanger thermally coupled to the ADIPregeneration section and configured to heat a seventh buffer streamusing heat carried by an ADIP regeneration section bottoms outletstream, a tenth heat exchanger thermally coupled to the natural gasde-colorizing section and configured to heat an eighth buffer streamusing heat carried by a natural gas de-colorizing section pre-flash drumoverhead outlet stream, an eleventh heat exchanger thermally coupled tothe natural gas de-colorizing section and configured to heat a ninthbuffer stream using heat carried by a natural gas de-colorizer overheadoutlet stream, a twelfth heat exchanger thermally coupled to the propanevapor recovery section and configured to heat a tenth buffer streamusing heat carried by a propane vapor recovery compressor outlet stream,and a thirteenth heat exchanger thermally coupled to the propane productrefrigeration section and configured to heat an eleventh buffer streamusing heat carried by a propane refrigeration compressor outlet streamfrom the propane product refrigeration section.

In another aspect combinable with any of the previous aspects, thesecond subset includes a third subset including one or more of themultiple heat exchangers thermally coupled to the third multiplesub-units of the NGL fractionation plant.

In another aspect combinable with any of the previous aspects, the thirdsubset includes a fourteenth heat exchanger thermally coupled to thepropane product sub-cooling and configured to heat a twelfth bufferstream using heat carried by a propane main compressor outlet streamfrom the propane product sub-cooling section, a fifteenth heat exchangerthermally coupled to the butane product refrigeration section andconfigured to heat a thirteenth buffer stream using heat carried by abutane refrigeration compressor outlet stream from the butane productrefrigeration section, a sixteenth heat exchanger thermally coupled tothe ethane production section and configured to heat a fourteenth bufferstream using heat carried by an ethane dryer outlet stream, and aseventeenth heat exchanger thermally coupled to the RVP control sectionand configured to heat a fifteenth buffer stream using heat carried by aRVP control column overhead outlet stream.

In another aspect combinable with any of the previous aspects, thebuffer stream is a first buffer stream of a first type. The multipleheat exchangers include a second heat exchanger thermally coupled to thede-propanizer section and configured to heat a second buffer stream of asecond type different from the first type using heat carried by thede-propanizer overhead outlet stream, and a fourth heat exchangerthermally coupled to the de-butanizer section, the fourth heat exchangerconfigured to heat the second buffer stream of the second type usingheat carried by the de-butanizer overhead outlet stream.

In another aspect combinable with any of the previous aspects, the firstbuffer stream of the first type includes oil and the second bufferstream of the second type includes water.

In another aspect combinable with any of the previous aspects, thesystem includes a first storage tank to store the first buffer streamand a second storage tank to store the second buffer stream.

In another aspect combinable with any of the previous aspects, thecontrol system is configured to flow the first buffer stream or thesecond buffer stream or both from the respective storage tank to theheat exchanger network.

In another aspect combinable with any of the previous aspects, the firstsub-system includes a modified Goswami cycle system configured toproduce power and sub-ambient cooling capacity using at least a portionof heat carried by the first buffer stream.

In another aspect combinable with any of the previous aspects, thesecond sub-system includes a modified multi-effect-distillation (MED)system configured to produce potable water using at least a portion ofheat carried by the third heat exchanger.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the detailed description. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of an example of a low grade waste heatrecovery system.

FIG. 1B is a schematic diagram of a propane de-hydrator section wasteheat recovery system in a NGL fractionation plant.

FIG. 1C is a schematic diagram of a de-propanizer section waste heatrecovery system in a NGL fractionation plant.

FIG. 1D is a schematic diagram of a butane de-hydrator section wasteheat recovery system in a NGL fractionation plant.

FIG. 1E is a schematic diagram of a de-butanizer section waste heatrecovery system in a NGL fractionation plant.

FIG. 1F is a schematic diagram of a de-pentanizer section waste heatrecovery system in a NGL fractionation plant.

FIG. 1G is a schematic diagram of an ADIP regeneration section wasteheat recovery system in a NGL fractionation plant.

FIG. 1H is a schematic diagram of a natural gas de-colorizing sectionwaste heat recovery system in a NGL fractionation plant.

FIG. 1I is a schematic diagram of a propane tank vapor recovery sectionwaste heat recovery system in a NGL fractionation plant.

FIG. 1J is a schematic diagram of a propane product refrigerationsection waste heat recovery system in a NGL fractionation plant.

FIG. 1K is a schematic diagram of a propane product sub-cooling sectionwaste heat recovery system in a NGL fractionation plant.

FIG. 1L is a schematic diagram of a butane product refrigeration sectionwaste heat recovery system in a NGL fractionation plant.

FIG. 1M is a schematic diagram of an ethane production section wasteheat recovery system in a NGL fractionation plant.

FIG. 1N is a schematic diagram of a natural gasoline vapor pressurecontrol section waste heat recovery system in a NGL fractionation plant.

FIG. 1O is a schematic diagram of a modified Goswami cycle.

FIG. 1P is a schematic diagram of a modified MED phase that includesmultiple trains.

DETAILED DESCRIPTION

NGL Plant

Gas processing plants can purify raw natural gas or crude oil productionassociated gases (or both) by removing common contaminants such aswater, carbon dioxide and hydrogen sulfide. Some of the substances whichcontaminate natural gas have economic value and can be processed or soldor both. Upon the separation of methane gas, which is useful as salesgas for houses and power generation, the remaining hydrocarbon mixturein liquid phase is called natural gas liquids (NGL). The NGL isfractionated in a separate plant or sometimes in the same gas processingplant into ethane, propane and heavier hydrocarbons for severalversatile uses in chemical and petrochemical as well as transportationindustries. The NGL fractionation plant uses the following processes orsections: fractionation, product treating, and natural gasolineprocessing. The fractionation processes or sections can include heatsources (also commonly referred to as streams) including, but notlimited to, a propane condenser, a propane refrigerant condenser, anaphtha cooler, a de-pentanizer condenser, an amine-di-iso-propanol(ADIP) cooler, a regenerator overhead (OVHD) condenser, a Reid vaporpressure (RVP) column condenser, a de-propanizer condenser, ade-butanizer condenser, or combinations thereof. The product treatingprocesses or sections can include the following non-limiting heatsources: a propane dehydrator condenser, a butane dehydrator condenser,a propane condenser, an air-cooled condenser, a regeneration gas cooler,and a butane condenser, or combinations thereof. The natural gasolineprocessing processes or sections can include, but are not limited to, anatural gasoline (NG) flash vapor condenser, a NG de-colorizercondenser, or combinations thereof.

Fractionation Section

Fractionation is the process of separating the different components ofnatural gas. Separation is possible because each component has adifferent boiling point. At temperatures less than than the boilingpoint of a particular component, that component condenses to a liquid.It is also possible to increase the boiling point of a component byincreasing the pressure. By using columns operating at differentpressures and temperatures, the NGL fractionation plant is capable ofseparating ethane, propane, butane, pentane, or combinations thereof(with or without heavier associated hydrocarbons) from NGL fractionationfeeds. De-ethanizing separates ethane from C2+NGL, where C2 refers to amolecule containing two carbon atoms (ethane), and where C2+ refers to amixture containing molecules having two or more carbon atoms, forexample, a NGL containing C2, C3, C4, C5 can be abbreviated as “C2+NGL”.De-propanizing and de-butanizing separate propane and butane,respectively, from C3+NGL and C4+NGL, respectively. Because the boilingpoints of heavier natural gases are closer to each other, such gases canbe harder to separate compared to lighter natural gases. Also, a rate ofseparation of heavier components is less than that of comparativelylighter components. In some instances, the NGL fractionation plant canimplement, for example, about 45 distillation trays in the de-ethanizer,about 50 trays in the de-propanizer, and about 55 trays in thede-butanizer.

The fractionation section can receive a feed gas containing C2+NGL fromgas plants, which are upstream plants that condition and sweeten thefeed gas, and produce a sales gas, such as a C1/C2 mixture, where C1 isabout 90%, as a final product. The C2+NGL from gas plants can be furtherprocessed in the NGL fractionation plant for C2+ recovery. From feedmetering or surge unit metering (or both), feed flows to the threefractionation modules, namely, the de-ethanizing module, thede-propanizing module and the de-butanizing module, each of which isdescribed later.

De-Ethanizer Module (or De-Ethanizer Column)

The C2+NGL is pre-heated before entering the de-ethanizer column forfractionation. The separated ethane leaves the column as overhead gas.The ethane gas is condensed by a closed-loop propane refrigerationsystem. After being cooled and condensed, the ethane is a mixture of gasand liquid. The liquid ethane is separated and pumped back to the top ofthe column as reflux. The ethane gas is warmed in an economizer and thensent to users. The bottoms product from the de-ethanizer reboiler isC3+NGL, which is sent to the de-propanizer module.

De-Propanizer Module (or De-Propanizer Column)

From the de-ethanizer module, C3+NGL enters the de-propanizer module forfractionation. The separated propane leaves the column as overhead gas.The gas is condensed using coolers. The propane condensate is collectedin a reflux drum. Some of the liquid propane is pumped back to thecolumn as reflux. The rest of the propane is either treated or sent tousers as untreated product. The bottoms product from the depropanizerreboiler, C4+ is then sent to the de-butanizer module

De-Butanizer Module (or De-Butanizer Column)

C4+ enters the de-butanizer module for fractionation. The separatedbutane leaves the column as overhead gas. The gas is condensed usingcoolers. The butane condensate is collected in a reflux drum. Some ofthe liquid butane is pumped back to the column as reflux. The rest ofthe butane is either treated or sent to users as untreated product. Thebottoms product from the debutanizer reboiler, C5+ natural gas (NG) goeson to a RVP control section (which may also be referred to as a rerununit), which will be discussed in greater detail in a later section.

Product Treating Section

While ethane requires no further treatment, propane and butane productsare normally treated to remove hydrogen sulfide (H₂S), carbonyl sulfide(COS), and mercaptan sulfur (RSH). Then, the products are dried toremove any water. All exported product is treated, while untreatedproducts can go to other industries. As described later, propanereceives ADIP treating, MEROX™ (Honeywell UOP; Des Plaines, Ill.)treating, and dehydration. Butane receives MEROX treating, anddehydration.

ADIP Treating Section

ADIP is a solution of di-isopropanol amine and water. ADIP treatingextracts H₂S and COS from propane. The ADIP solution, through contactwith the sour propane, absorbs the H₂S and COS. The ADIP solution firstcontacts the sour propane in an extractor. In the extractor, the ADIPabsorbs most of the H₂Sand some of the COS. The propane then passesthrough a mixer/settler train where the propane contacts with ADIPsolution to extract more H₂Sand COS. This partially sweetened propane iscooled and then washed with water to recover the ADIP entrained with thepropane. The propane is then sent to MEROX treating, which is describedlater. The rich ADIP that has absorbed the H₂Sand COS leaves the bottomof the extractor and is regenerated into lean ADIP for reuse. Theregenerator column has a temperature and pressure that are suitable foracid gas removal. When the rich ADIP enters the regenerator, theentrained acid gases are stripped. As the acid gases leaves theregenerator as overhead, any free water is removed to prevent acidformation. The acid gases are then sent to flare. The lean ADIP leavesthe extractor bottom and is cooled and filtered. Lean ADIP returns tothe last mixer/settler and flows back through the system in thecounter-current direction of the propane to improve contact between thepropane and ADIP, which improves H₂S and COS extraction.

C3/C4 MEROX Treating Section

MEROX treating removes mercaptan sulfur from C3/C4 product. Mercaptansare removed using a solution of sodium hydroxide (NaOH), also known bythe commercial name caustic soda (hereinafter referred to as “caustic”)and MEROX. The MEROX catalyst facilitates the oxidation of mercaptans todisulfides. The oxidation takes place in an alkaline environment, whichis provided by using the caustic solution. MEROX treating for C3 and C4is similar. Both products are prewashed with caustic to remove anyremaining traces of H₂S, COS, and CO₂. This prevents damage to thecaustic that is used in MEROX treating. After prewashing, product flowsto an extractor, where a caustic solution with MEROX catalyst contactswith the product. The caustic/catalyst solution converts the mercaptansinto mercaptides. The sweetened product, which is lean on acid gases,leaves the extractor as overhead and any remaining caustic is separated.Caustic leaves the bottom of both product extractors rich withmercaptides. The rich caustic is regenerated into lean caustic forreuse. The C3/C4 extraction sections share a common caustic regenerationsection, namely, an oxidizer. Before entering the bottom of theoxidizer, the rich caustic is injected with MEROX catalyst to maintainproper catalyst concentration, heated, and mixed with process air. Inthe oxidizer, the mercaptides are oxidized into disulfides. The mixtureof disulfides, caustic, and air leave the oxidizer as overhead. The air,disulfide gases, and disulfide oil are separated from the regeneratedcaustic. The regenerated caustic is pumped to the C3/C4 extractor.Regenerated caustic with any residual disulfides is washed with NG inthe NG wash settler.

C3/C4 Dehydration Section

Propane or butane products (or both) contain water when they leave MEROXtreating. Dehydration removes moisture in such products throughadsorption before the products flow to refrigeration and storage. Thedehydration processes for C3 and C4 are similar. Both C3/C4 dehydrationsections have two de-hydrators containing molecular sieve desiccantbeds. One de-hydrator is in service while the other undergoesregeneration. Regeneration consists of heating the sieve beds to removemoisture, then cooling the beds before reuse. During drying, productflows up and through the molecular sieve bed, which adsorbs (that is,binds to its surface) moisture. From the top of the de-hydrator, dryC3/C4 products flow to refrigeration.

Natural Gasoline (NG) Processing Section

NG processing includes RVP control, de-colorizing and de-pentanizingsections.

RVP Control Section

A Reid vapor pressure (RVP) control section (or rerun unit) is afractionator column that receives the C5+NG from the debutanizer bottom.The RVP control section collects a pentane product. The RVP controlsection can be used to adjust the RVP of the pentane product at a rerunfractionator overhead before the pentane product is sent to a pentanestorage tank. RVP is a measure of the ability of a hydrocarbon tovaporize. RVP (sometimes called volatility) is an importantspecification in gasoline blending. The RVP control section stabilizesthe RVP of NG by removing small amounts of pentane. Depending onoperational requirements, the RVP control section can be totally orpartially bypassed. NG from the debutanizer bottoms goes to the RVPcolumn where a controlled amount of pentane is stripped and leaves thecolumn as overhead gas. As in NGL fractionation, the overhead gas iscondensed with coolers, and some of the condensate is pumped back to thecolumn as reflux. The remaining pentane is cooled and sent to storage.If the RVP column bottoms product (NG) meets color specifications, it issent to storage. If not, it is sent to decolorizing.

De-Colorizing Section

The de-colorizing section removes color bodies from NG. Color bodies aretraces of heavy ends found in the de-butanizer bottoms product. Otherimpurities such as corrosion products from the pipeline may also bepresent. These must be removed for NG to meet the color specification.De-colorizer feed can be RVP column bottoms product or de-butanizerbottoms product, or a combination of both. Additional natural gasolinecan also be supplied from other facilities to maintain a hexane plus(C6+) product supply. If de-colorizing is needed, NG first passesthrough a pre-flash-drum. A large portion of the lighter NG componentsvaporizes and leaves the drum as overhead. The heavier NG componentsremain along with the color bodies and are fed to the de-colorizercolumn, where the remaining color bodies are separated. The NG leavesthe de-colorizer as overhead gas and is condensed and collected in theNG product drum, with some pumped back to the column as reflux. Overheadfrom the column and flash drum are joined and pumped to either thede-pentanizer (described later) or cooled and sent to storage in thefeed product surge unit. The color bodies leave the de-colorizer asbottoms product and are pumped to the feed and surge unit to be injectedinto a crude line.

De-Pentanizing Section

De-pentanizing uses a fractionation column to produce a pentane overheadproduct and a C6+ bottoms product. Both the pentane product and the C6+bottoms product are separately fed to storage or downstream thepetrochemical plants. The feed to the de-pentanizer is the NG productstream from the de-colorizing section. Feed can be increased ordecreased based on the demand for C6+ bottoms product. If the NGLfractionation plant NG production cannot meet demand, NG can be importedfrom oil refineries. The de-colorized NG is preheated before enteringthe de-pentanizer. The separated pentane leaves the column as overheadgas. The overhead condensers cool the overhead stream, and some ispumped back to the column as reflux. The remaining pentane is cooled andsent to storage. Light NG in the bottoms is vaporized and returned toheat the de-pentanizer. The remaining bottoms product is cooled and sentto storage as C6+.

Table 2 lists duty per train of major waste heat streams in an exampleof an NGL fractionation plant.

TABLE 2 Duty/train Stream Name (MMBtu/h) Propane refrigerant condenser94 Propane de-hydration condenser 22 Butane de-hydrator condenser 9Naphtha cooler 11 De-pentanizer condenser 100 ADIP cooler 73 RegeneratorOVHD condenser 18 NG flash vapor condenser 107 NG de-colorizer condenser53 Natural gasoline (cooling) process 29 propane condenser Fractionationpropane condenser 81 Air cooled condenser 16 Regeneration gas cooler 22RVP column condenser 36 Butane condenser 49 De-propanizer condenser 194De-butanizer condenser 115

In Table 2, “Duty/train” represents each stream's thermal duty inmillions Btu per hour (MMBtu/h) per processing train. A typical NGLfractionation plant includes three to four processing trains.

The systems described in this disclosure can be integrated with a NGLfractionation plant to make the fractionation plant more energyefficient or less polluting or both. In particular, the energyconversion system can be implemented to recover low grade waste heatfrom the NGL fractionation plant. Low grade waste heat is characterizedby a temperature difference between a source and sink of the low gradeheat steam being between 65° C. and 232° C. (150° F. and 450° F.). TheNGL fractionation plant is an attractive option for integration withenergy conversion systems due to a large amount of low grade waste heatgenerated by the plant and an absence of a need for deep cooling. Deepcooling refers to a temperature that is less than ambient that uses arefrigeration cycle to maintain.

The low grade waste heat from an NGL fractionation plant can be used forcommodities such as carbon-free power generation, cooling capacitygeneration, potable water production from sea water, or combinationsthereof. Low grade waste heat is characterized by a temperature rangingbetween 65° C. and 232° C. (150° F. to 450° F.). The waste heat can beused for the mono-generation, co-generation, or tri-generation of one ormore or all of the commodities mentioned earlier. Low grade waste heatfrom the NGL fractionation plant can be used to provide in-plantsub-ambient cooling, thus reducing the consumption of power or fuel (orboth) of the plant. Low grade waste heat from the NGL fractionationplant can be used to provide ambient air conditioning or cooling in theindustrial community or in a nearby non-industrial community, thushelping the community to consume energy from alternative sources. Inaddition, the low grade waste heat can be used to desalinate water andproduce potable water to the plant and adjacent community. An NGLfractionation plant is selected for low grade waste heat recoverybecause of a quantity of low grade waste heat available from the NGLfractionation plant as well as a cooling requirement of the plant toambient temperature cooling (instead of deep cooling).

The energy conversion systems described in this disclosure can beintegrated into an existing NGL fractionation plant as a retrofit or canbe part of a newly constructed NGL fractionation plant. A retrofit to anexisting NGL fractionation plant allows the carbon-free powergeneration, and fuel savings advantages offered by the energy conversionsystems described here to be accessible with a reduced capitalinvestment. For example, the energy conversion systems described herecan produce one or more or all of substantially between 35 MW and 40 MW(for example, 37 MW) of carbon-free power, substantially between 100,000and 150,000 m³/day (for example, 120,000 m³/day) of desalinated water,and substantially between 350 MM BTU/h and 400 MM BTU/h (for example,388 MM BTU/h) of cooling capacity for in-plant or community utilizationor both.

As described later, the systems for waste heat recovery and re-use fromthe NGL fractionation plant can include modified multi-effectdistillation (MED) systems, customized Organic Rankine Cycle (ORC)systems, unique ammonia-water mixture Kalina cycle systems, customizedmodified Goswami cycle systems, mono-refrigerant specific vaporcompression-ejector-expander triple cycle systems, or combinations ofone or more of them. Details of each disclosure are described in thefollowing paragraphs.

Heat Exchangers

In the configurations described in this disclosure, heat exchangers areused to transfer heat from one medium (for example, a stream flowingthrough a plant in a NGL fractionation plant, a buffer fluid or suchmedium) to another medium (for example, a buffer fluid or differentstream flowing through a plant in the NGL fractionation plant). Heatexchangers are devices which transfer (exchange) heat typically from ahotter fluid stream to a relatively less hotter fluid stream. Heatexchangers can be used in heating and cooling applications, for example,in refrigerators, air conditions or such cooling applications. Heatexchangers can be distinguished from one another based on the directionin which fluids flow. For example, heat exchangers can be parallel-flow,cross-flow or counter-current. In parallel-flow heat exchangers, bothfluid involved move in the same direction, entering and exiting the heatexchanger side-by-side. In cross-flow heat exchangers, the fluid pathruns perpendicular to one another. In counter-current heat exchangers,the fluid paths flow in opposite directions, with one fluid exitingwhether the other fluid enters. Counter-current heat exchangers aresometimes more effective than the other types of heat exchangers.

In addition to classifying heat exchangers based on fluid direction,heat exchangers can also be classified based on their construction. Someheat exchangers are constructed of multiple tubes. Some heat exchangersinclude plates with room for fluid to flow in between. Some heatexchangers enable heat exchange from liquid to liquid, while some heatexchangers enable heat exchange using other media.

Heat exchangers in a NGL fractionation plant are often shell and tubetype heat exchangers which include multiple tubes through which fluidflows. The tubes are divided into two sets—the first set contains thefluid to be heated or cooled; the second set contains the fluidresponsible for triggering the heat exchange, in other words, the fluidthat either removes heat from the first set of tubes by absorbing andtransmitting the heat away or warms the first set by transmitting itsown heat to the fluid inside. When designing this type of exchanger,care must be taken in determining the correct tube wall thickness aswell as tube diameter, to allow optimum heat exchange. In terms of flow,shell and tube heat exchangers can assume any of three flow pathpatterns.

Heat exchangers in NGL facilities can also be plate and frame type heatexchangers. Plate heat exchangers include thin plates joined togetherwith a small amount of space in between, often maintained by a rubbergasket. The surface area is large, and the corners of each rectangularplate feature an opening through which fluid can flow between plates,extracting heat from the plates as it flows. The fluid channelsthemselves alternate hot and cold liquids, meaning that the heatexchangers can effectively cool as well as heat fluid. Because plateheat exchangers have large surface area, they can sometimes be moreeffective than shell and tube heat exchangers.

Other types of heat exchangers can include regenerative heat exchangersand adiabatic wheel heat exchangers. In a regenerative heat exchanger,the same fluid is passed along both sides of the exchanger, which can beeither a plate heat exchanger or a shell and tube heat exchanger.Because the fluid can get very hot, the exiting fluid is used to warmthe incoming fluid, maintaining a near constant temperature. Energy issaved in a regenerative heat exchanger because the process is cyclical,with almost all relative heat being transferred from the exiting fluidto the incoming fluid. To maintain a constant temperature, a smallquantity of extra energy is needed to raise and lower the overall fluidtemperature. In the adiabatic wheel heat exchanger, an intermediateliquid is used to store heat, which is then transferred to the oppositeside of the heat exchanger. An adiabatic wheel consists of a large wheelwith threads that rotate through the liquids—both hot and cold—toextract or transfer heat. The heat exchangers described in thisdisclosure can include any one of the heat exchangers described earlier,other heat exchangers, or combinations of them.

Each heat exchanger in each configuration can be associated with arespective thermal duty (or heat duty). The thermal duty of a heatexchanger can be defined as an amount of heat that can be transferred bythe heat exchanger from the hot stream to the cold stream. The amount ofheat can be calculated from the conditions and thermal properties ofboth the hot and cold streams. From the hot stream point of view, thethermal duty of the heat exchanger is the product of the hot stream flowrate, the hot stream specific heat, and a difference in temperaturebetween the hot stream inlet temperature to the heat exchanger and thehot stream outlet temperature from the heat exchanger. From the coldstream point of view, the thermal duty of the heat exchanger is theproduct of the cold stream flow rate, the cold stream specific heat anda difference in temperature between the cold stream outlet from the heatexchanger and the cold stream inlet temperature from the heat exchanger.In several applications, the two quantities can be considered equalassuming no heat loss to the environment for these units, particularly,where the units are well insulated. The thermal duty of a heat exchangercan be measured in watts (W), megawatts (MW), millions of BritishThermal Units per hour (Btu/hr), or millions of kilocalories per hour(Kcal/h). In the configurations described here, the thermal duties ofthe heat exchangers are provided as being “about X MW,” where “X”represents a numerical thermal duty value. The numerical thermal dutyvalue is not absolute. That is, the actual thermal duty of a heatexchanger can be approximately equal to X, greater than X or less thanX.

Flow Control System

In each of the configurations described later, process streams (alsocalled “streams”) are flowed within each plant in a NGL fractionationplant and between plants in the NGL fractionation plant. The processstreams can be flowed using one or more flow control systems implementedthroughout the NGL fractionation plant. A flow control system caninclude one or more flow pumps to pump the process streams, one or moreflow pipes through which the process streams are flowed and one or morevalves to regulate the flow of streams through the pipes.

In some implementations, a flow control system can be operated manually.For example, an operator can set a flow rate for each pump and set valveopen or close positions to regulate the flow of the process streamsthrough the pipes in the flow control system. Once the operator has setthe flow rates and the valve open or close positions for all flowcontrol systems distributed across the NGL fractionation plant, the flowcontrol system can flow the streams within a plant or between plantsunder constant flow conditions, for example, constant volumetric rate orsuch flow conditions. To change the flow conditions, the operator canmanually operate the flow control system, for example, by changing thepump flow rate or the valve open or close position.

In some implementations, a flow control system can be operatedautomatically. For example, the flow control system can be connected toa computer system to operate the flow control system. The computersystem can include a computer-readable medium storing instructions (suchas flow control instructions and other instructions) executable by oneor more processors to perform operations (such as flow controloperations). An operator can set the flow rates and the valve open orclose positions for all flow control systems distributed across the NGLfractionation plant using the computer system. In such implementations,the operator can manually change the flow conditions by providing inputsthrough the computer system. Also, in such implementations, the computersystem can automatically (that is, without manual intervention) controlone or more of the flow control systems, for example, using feedbacksystems implemented in one or more plants and connected to the computersystem. For example, a sensor (such as a pressure sensor, temperaturesensor or other sensor) can be connected to a pipe through which aprocess stream flows. The sensor can monitor and provide a flowcondition (such as a pressure, temperature, or other flow condition) ofthe process stream to the computer system. In response to the flowcondition exceeding a threshold (such as a threshold pressure value, athreshold temperature value, or other threshold value), the computersystem can automatically perform operations. For example, if thepressure or temperature in the pipe exceeds the threshold pressure valueor the threshold temperature value, respectively, the computer systemcan provide a signal to the pump to decrease a flow rate, a signal toopen a valve to relieve the pressure, a signal to shut down processstream flow, or other signals.

In some implementations, the techniques described here can beimplemented using a waste heat recovery network that includes 17 heatexchanger units distributed in specific areas in the NGL fractionationplant and a utility plant to heat high pressure buffer streams. A 1^(st)buffer stream is hot oil. The heated oil is used for generating powerusing a modified Goswami Cycle. A 2^(nd) buffer stream is high pressurewater. The heated water is used to generate potable water from saltwater using a MED system. The modified Goswami Cycle is coupled to 15 ofthe 17 heat exchanger units in the network and uses the 1^(st) bufferstream. The MED system is coupled to the two remaining heat exchangerunit and uses the 2^(nd) buffer stream. In some implementations, theheat recovered from the streams of the NGL fractionation plant can beused to operate the modified Goswami Cycle alone or the MED systemalone. In some implementations, the heat can be used to operate both themodified Goswami Cycle and the MED system. In some implementations, the1^(st) and 2^(nd) buffer streams can be the same buffer stream havingthe same composition and stored in the same storage tank/storage unit.

The techniques can be implemented to increase the temperature of thefirst buffer fluid stream from a temperature of between 115° F. and 125°F. (for example, about 120° F.) to a temperature between 180° F. and190° F. (for example, about 187° F.). The first buffer fluid stream isthen used to drive a modified Goswami cycle system to produce between 20MW and 30 MW (for example, 26 MW) of power and between 60 MM Btu/h and70 MM Btu/h (for example, about 63 MM Btu/h) of sub-ambient cooling. Thefirst buffer fluid stream temperature is reduced in the modified Goswamicycle system to between 115° F. and 125° F. (for example, 120° F.), andthe stream is flowed back to the first buffer fluid stream storage tank.The techniques can be implemented to increase the temperature of thesecond buffer fluid stream from a temperature of between 115° F. and125° F. (for example, about 120° F.) to a temperature between 130° F.and 140° F. (for example, about 136° F.). The second buffer fluid streamis then used to drive a modified MED system to produce about 32,000m³/day of potable water. The second buffer fluid stream temperature isreduced in the MED system to between 115° F. and 125° F. (for example,120° F.), and the stream is flowed back to the second buffer fluidstream storage tank.

FIG. 1A is a schematic diagram of an example of a low grade waste heatrecovery system. The schematic includes a storage tank 1305 to storebuffer fluid of a 1^(st) type, for example, oil, pressurized water, orsuch buffer fluid. The schematic also includes a storage tank 1309 tostore buffer fluid of a 2^(nd) type, for example, pressurized water,oil, or such buffer fluid. In some implementations, the buffer fluid ofthe 1^(st) type is of a different composition from the buffer fluid ofthe 2^(nd) type. The buffer fluid from the storage tank 1305 and thestorage tank 1309 are flowed to a heat exchanger network 1307 which, insome implementations, can include 17 heat exchangers (for example, heatexchangers 13 a, 13 b, 13 c, 13 d, 13 e, 13 f, 13 g, 13 h, 13 i, 13 j,13 k, 13 l, 13 m, 13 n, 13 o, 13 p, 13 q), which are described in detaillater. The buffer fluids are flowed through the heat exchanger network1307 and heated by streams in the NGL fractionation plant (describedlater). As described later, the heated buffer fluid from the storagetank 1305 is used to generate power and sub-ambient cooling capacity ina modified Goswami cycle system 1313, and the heated buffer fluid fromthe storage tank 1309 is used to generate potable water in a modifiedMED system 1311. The buffer fluids are then returned to their respectivestorage tanks. In some implementations, the waste heat recovery systemcan be implemented to include either only the modified Goswami cyclesystem 1313 or the modified MED system 1311.

In some implementations, the buffer fluid of the 1^(st) type and thebuffer fluid of the 2^(nd) type are the same buffer fluid having thesame composition. In such implementations, the buffer fluid can beflowed from a single storage tank. A stream of the buffer fluid can beused to generate power and sub-ambient cooling capacity in the modifiedGoswami cycle system 1313, and another stream of the buffer fluid can beused to generate potable water in the modified MED system 1311. Thebuffer fluids can then be returned to the common storage tank.

FIG. 1B is a schematic diagram of a propane de-hydrator section wasteheat recovery system in the NGL fractionation plant. A 1^(st) heatexchanger 13 a is located in the propane de-hydrator section of the NGLfractionation plant. The first buffer fluid stream flows from thestorage tank 1305 to the 1^(st) heat exchanger 13 a to cool down thepropane de-hydrator outlet stream. In turn, the temperature of the firstbuffer fluid stream increases to between 390° F. and 400° F. (forexample, 395° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 1^(st) heatexchanger 13 a is between 90 MM Btu/h and 100 MM Btu/h (for example,about 96 MM Btu/h).

FIG. 1C is a schematic diagram of a de-propanizer section waste heatrecovery system in the NGL fractionation plant. A 2^(nd) heat exchanger13 b is located in the de-propanizer section of the NGL fractionationplant. In some implementations, the buffer fluid in the storage tank1309 is pressurized water at a temperature of between 115° F. and 125°F. (for example, 120° F.). The second buffer fluid stream flows from thestorage tank 1309 to the 2^(nd) heat exchanger 13 b to cool down thede-propanizer overhead outlet stream. In turn, the temperature of thesecond buffer fluid stream increases to between 130° F. and 140° F. (forexample, 136° F.). The second buffer fluid stream is flowed to the firsttrain of the MED system 1311 (described later). The total thermal dutyof the 2^(nd) heat exchanger 13 b is between 945 MM Btu/h and 955 MMBtu/h (for example, about 951 MM Btu/h).

FIG. 1D is a schematic diagram of a butane de-hydrator section wasteheat recovery system in the NGL fractionation plant. A 3^(rd) heatexchanger 13 c is located in the butane de-hydrator section of the NGLfractionation plant. The first buffer fluid stream flows from thestorage tank 1305 to the 3^(rd) heat exchanger 13 c to cool down thebutane de-hydrator outlet stream. In turn, the temperature of the firstbuffer fluid stream increases to between 390° F. and 400° F. (forexample, 395° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 3^(rd) heatexchanger 13 c is between 40 MM Btu/h and 50 MM Btu/h (for example,about 47 MM Btu/h).

FIG. 1E is a schematic diagram of a de-butanizer section waste heatrecovery system in the NGL fractionation plant. A 4^(th) heat exchanger13 d is located in the de-butanizer section of the NGL fractionationplant. In some implementations, the second buffer fluid in the storagetank 1309 (namely, water) at a temperature of between 115° F. and 125°F. (for example, 120° F.) flows from the storage tank 1309 to the 4^(th)heat exchanger 13 d to cool down the de-butanizer overhead outletstream. In turn, the temperature of the second buffer fluid streamincreases to between 150° F. and 160° F. (for example, 152° F.). Thesecond buffer fluid stream flows to the collection header to join othersecond buffer fluid streams to flow to the modified MED system 1311(described later). The total thermal duty of the 4^(th) heat exchanger13 d is between 65 MM Btu/h and 75 MM Btu/h (for example, about 69 MMBtu/h).

A 5^(th) heat exchanger 13 e is located in the de-butanizer section ofthe NGL fractionation plant. In some implementations, the first bufferfluid in the storage tank 1305 (namely, oil) at a temperature of between115° F. and 125° F. (for example, 120° F.) flows from the storage tank1305 to the 5^(th) heat exchanger 13 e to cool down the de-butanizeroverhead outlet stream. In turn, the temperature of the first bufferfluid stream increases to between 150° F. and 160° F. (for example, 152°F.). The first buffer fluid stream is flowed to the collection header tojoin other first buffer fluid streams to flow to the modified Goswamicycle 1313. The total thermal duty of the 5^(th) heat exchanger 13 e isbetween 515 MM Btu/h and 525 MM Btu/h (for example, about 518 MM Btu/h).

A 6^(th) heat exchanger 13 f is located in the de-butanizer section ofthe NGL fractionation plant. In some implementations, the first bufferfluid stream flows from the storage tank 1305 to the 6^(th) heatexchanger 13 f to cool down the de-butanizer bottoms outlet stream. Inturn, the temperature of the first buffer fluid stream increases tobetween 255° F. and 265° F. (for example, 261° F.). The first bufferfluid stream flows to the collection header to join other first bufferfluid streams to flow to the modified cycle system 1313. The totalthermal duty of the 6^(th) heat exchanger 13 f is between 50 MM Btu/hand 60 MM Btu/h (for example, about 56 MM Btu/h).

FIG. 1F is a schematic diagram of a de-pentanizer section waste heatrecovery system in the NGL fractionation plant. A 7^(th) heat exchanger13 g is located in the de-pentanizer section of the NGL fractionationplant. In some implementations, the first buffer fluid stream flows fromthe storage tank 1305 to the 7^(th) heat exchanger 13 g to cool down thede-pentanizer overhead outlet stream. In turn, the temperature of thefirst buffer fluid stream increases to between 160° F. and 170° F. (forexample, 165° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 7^(th) heatexchanger 13 g is between 95 MM Btu/h and 105 MM Btu/h (for example,about 100 MM Btu/h).

FIG. 1G is a schematic diagram of an ADIP regeneration section wasteheat recovery system in the NGL fractionation plant. An 8^(th) heatexchanger 13 h is located in the ADIP regeneration section of the NGLfractionation plant. In some implementations, the first buffer fluidstream flows from the storage tank 1305 to the 8^(th) heat exchanger 13h to cool down the ADIP regeneration section overhead outlet stream. Inturn, the temperature of the first buffer fluid stream increases tobetween 220° F. and 230° F. (for example, 227° F.). The first bufferfluid stream flows to the collection header to join other first bufferfluid streams to flow to the modified Goswami system 1313. The totalthermal duty of the 8^(th) heat exchanger 13 h is between 15 MM Btu/hand 25 MM Btu/h (for example, about 18 MM Btu/h).

A 9^(th) heat exchanger 13 i is located in the ADIP regeneration sectionof the NGL fractionation plant. The first buffer fluid stream flows fromthe storage tank 1305 to the 9^(th) heat exchanger 13 i to cool down theADIP regeneration section bottoms outlet stream. In turn, thetemperature of the first buffer fluid stream increases to between 165°F. and 175° F. (for example, 171° F.). The first buffer fluid streamflows to the collection header to join other first buffer fluid streamsto flow to the modified Goswami cycle system 1313. The total thermalduty of the 9^(th) heat exchanger 13 i is between 215 MM Btu/h and 225MM Btu/h (for example, about 219 MM Btu/h).

FIG. 1H is a schematic diagram of a natural gas de-colorizing sectionwaste heat recovery system in the NGL fractionation plant. A 10^(th)heat exchanger 13 j is located in the natural gas de-colorizing sectionof the NGL fractionation plant. In some implementations, the firstbuffer fluid stream flows from the storage tank 1305 to the 10^(th) heatexchanger 13 j to cool down the natural gas de-colorizing sectionpre-flash drum overhead outlet stream. In turn, the temperature of thefirst buffer fluid stream increases to between 205° F. and 215° F. (forexample, 211° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 13^(th) heatexchanger 13 j is between 100 MM Btu/h and 110 MM Btu/h (for example,about 107 MM Btu/h).

An 11^(th) heat exchanger 13 k is located in the natural gasde-colorizing section of the NGL fractionation plant. In someimplementations, the first buffer fluid stream flows from the storagetank 1305 to the 11^(th) heat exchanger 13 k to cool down the naturalgas de-colorizer overhead outlet stream. In turn, the temperature of thefirst buffer fluid stream increases to between 225° F. and 235° F. (forexample, 229° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 11^(th) heatexchanger 13 k is between 50 MM Btu/h and 60 MM Btu/h (for example,about 53 MM Btu/h).

FIG. 1I is a schematic diagram of a propane tank vapor recovery sectionwaste heat recovery system in the NGL fractionation plant. A 12^(th)heat exchanger 13 l is located in the propane tank vapor recoverysection of the NGL fractionation plant. In some implementations, thefirst buffer fluid stream flows from the storage tank 1305 to the12^(th) heat exchanger 13 l to cool down the propane vapor recoverycompressor outlet stream. In turn, the temperature of the first bufferfluid stream increases to between 255° F. and 265° F. (for example, 263°F.). The first buffer fluid streams flows to the collection header tojoin other first buffer fluid streams to flow to the modified Goswamicycle system 1313. The total thermal duty of the 12^(th) heat exchanger13 l is between 25 MM Btu/h and 35 MM Btu/h (for example, about 29 MMBtu/h).

FIG. 1J is a schematic diagram of a propane product refrigerationsection waste heat recovery system in the NGL fractionation plant. A13^(th) heat exchanger 13 m is located in the propane productrefrigeration section of the NGL fractionation plant. In someimplementations, the first buffer fluid stream flows from the storagetank 1305 to the 13^(th) heat exchanger 13 m to cool down the propanerefrigeration compressor outlet stream. In turn, the temperature of thefirst buffer fluid stream increases to between 185° F. and 195° F. (forexample, 192° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 13^(th) heatexchanger 13 m is between 75 MM Btu/h and 85 MM Btu/h (for example,about 81 MM Btu/h).

FIG. 1K is a schematic diagram of a propane product sub-cooling sectionwaste heat recovery system in the NGL fractionation plant. A 14^(th)heat exchanger 13 n is located in the propane product sub-coolingsection of the NGL fractionation plant. In some implementations, thefirst buffer fluid stream flows from the storage tank 1305 to the14^(th) heat exchanger 13 n to cool down the propane main compressoroutlet stream. In turn, the temperature of the first buffer fluid streamincreases to between 235° F. and 245° F. (for example, 237° F.). Thefirst buffer fluid stream flows to the collection header to join otherfirst buffer fluid streams to flow to the modified Goswami cycle system1313. The total thermal duty of the 14^(th) heat exchanger 13 n isbetween 60 MM Btu/h and 70 MM Btu/h (for example, about 65 MM Btu/h).

FIG. 1L is a schematic diagram of a butane product refrigeration sectionwaste heat recovery system in the NGL fractionation plant. A 15^(th)heat exchanger 13 o is located in the butane product refrigerationsection of the NGL fractionation plant. In some implementations, thefirst buffer fluid stream flows from the storage tank 1305 to the15^(th) heat exchanger 13 o to cool down the butane refrigerationcompressor outlet stream. In turn, the temperature of the first bufferfluid stream increases to between 140° F. and 150° F. (for example, 147°F.). The first buffer fluid stream flows to the collection header tojoin other first buffer fluid streams to flow to the modified Goswamicycle system 1313. The total thermal duty of the 15^(th) heat exchanger13 o is between 45 MM Btu/h and 55 MM Btu/h (for example, about 49 MMBtu/h).

FIG. 1M is a schematic diagram of an ethane production section wasteheat recovery system in the NGL fractionation plant. A 16^(th) heatexchanger 13 p is located in the ethane production section of the NGLfractionation plant. In some implementations, the first buffer fluidstream flows from the storage tank 1305 to the 16^(th) heat exchanger 13p to cool down the ethane dryer outlet stream. In turn, the temperatureof the first buffer fluid stream increases to between 405° F. and 415°F. (for example, 410° F.). The first buffer fluid stream flows to thecollection header to join other first buffer fluid streams to flow tothe modified Goswami cycle system 1313. The total thermal duty of the16^(th) heat exchanger 13 p is between 15 MM Btu/h and 25 MM Btu/h (forexample, about 22 MM Btu/h).

FIG. 1N is a schematic diagram of a natural gasoline vapor pressurecontrol section waste heat recovery system in the NGL fractionationplant. A 17^(th) heat exchanger 13 q is located in the natural gasolinevapor pressure control section of the NGL fractionation plant. In someimplementations, the first buffer fluid stream flows from the storagetank 1305 to the 17^(th) heat exchanger 13 q to cool down the RVPcontrol column overhead outlet stream. In turn, the temperature of thefirst buffer fluid stream increases to between 205° F. and 215° F. (forexample, 211° F.). The first buffer fluid stream flows to the collectionheader to join other first buffer fluid streams to flow to the modifiedGoswami cycle system 1313. The total thermal duty of the 17^(th) heatexchanger 1 eq is between 30 MM Btu/h and 40 MM Btu/h (for example,about 36 MM Btu/h).

FIG. 1O is a schematic diagram of a modified Goswami cycle 1313. In someimplementations, the modified Goswami cycle 1313 can be implemented togenerate power ranging up to about 10 MW (for example, about 5 MW) andsub-ambient cooling capacity of between 380 MM Btu/h and 390 MM Btu/h(for example, about 388 MM Btu/h). Such sub-ambient cooling capacity cansave between 40 MW and 50 MW (for example, about 47 MW) of powercurrently used in the NGL fractionation plant due to the use ofconventional propane refrigeration package for the plant de-ethanizeroverhead stream condensation.

The modified Goswami cycle system 1313 can use specific mixtures ofammonia and water streams (for example, mixtures in the ratio of 50% to50% ammonia to water stream) at defined pressures in a heat exchangernetwork including four heat exchangers (for example, heat exchangers1312 a, 1312 b, 1312 c and 1312 d) and three coolers simultaneouslysatisfy specific cooling capacity in the NGL fractionation plantde-ethanizer overhead stream condensation and to generate power. Theammonia-water mixture is divided into two branches at about 11.5 bar.These two branches are heated and partially vaporized using thermalenergy of between about 1400 MM Btu/h and 1600 MM Btu/h (for example,1500 MM Btu/h) of waste heat from the buffer fluid flowed to themodified Goswami cycle 1313 from the heat exchanger network 1307, andbetween about 390 MM Btu/h and 400 MM Btu/h (for example, about 392 MMBtu/h) from the modified Goswami cycle separator bottom stream. TheGoswami cycle heat exchangers network configuration is in a parallelconfiguration with two heat exchangers in series in each branch for theammonia-water stream path.

The thermal duty of the first Goswami heat exchanger 1312 a rangesbetween about 510 MM Btu/h and 520 MM Btu/h (for example, 517 MM Btu/h).The thermal duty of the second Goswami heat exchanger 1312 b rangesbetween about 710 MM Btu/h and 720 MM Btu/h (for example, 714 MM Btu/h).The thermal duty of the third Goswami heat exchanger 1312 c rangesbetween about 265 MM Btu/h and 275 MM Btu/h (for example, 271 MM Btu/h).The thermal duty of the fourth Goswami heat exchanger 1312 d rangesbetween about 385 MINI Btu/h and 395 MM Btu/h (for example, 392 MMBtu/h). The ammonia-water liquid stream is partially vaporized in thefour Goswami heat exchangers and separated to high ammonia concentratedvapor stream. A portion of the high ammonia concentrated vapor stream(for example, about 27%) is flowed to the turbine at high pressure whereit is expanded to lower pressure of between about 2 bar and 5 bar (forexample, about 4.3 bar) to generate power between about 1 MW and 5 MW(for example, 4 MW). The remainder of the high ammonia concentratedvapor stream (for example, about 73%) is flowed to the first watercooler for condensation at high pressure and then throttled in athrottling valve to lower pressure to about 4.3 bar to generate coolingcapacity. The condensed stream at a temperature of about 37° F. is usedfor the in-plant cooling of the NGL fractionation plant in thede-ethanizer section to save mechanical compression, thereby savingthermal energy of about 388 MM Btu/h (for example, about 47 MW ofpower).

The high water concentration liquid stream out from the separator isused in a hydraulic pump to generate about 1.0 MW of power. The threeammonia-water vapor streams are then merged together in one stream thatis then condensed in a second water cooler using water stream at atemperature of about 77° F. to continue the cycle. The first bufferfluid stream at a temperature ranging between about 180° F. and 190° F.(for example, about 187° F.) is used to pre-heat and partially vaporizethe ammonia-water liquid feed (at a temperature ranging between about 10bar and 20 bar (for example, about 11.5 bar) and a temperature rangingbetween about 80° F. and 90° F. (for example, about 87° F.)). The hotoil temperature is then flowed back to the storage tank 1305 to continuethe waste heat recovery cycle in the NGL fractionation plant asdescribed earlier.

FIG. 1P shows a first MED phase 1311 that includes three trains. Thefirst train 1320 a can include 4 effects connected in series. The secondtrain 1320 b can include 3 effects connected in series. The third train1320 c can include 2 effects connected in series. The number of trainsand the number of effects in this implementation are examples. The MEDsystem 1311 can be implemented to include one or more phases, with eachphase having fewer or more trains, each train having fewer or moreeffects. The arrangement shown in FIG. 1P represents a best matchbetween the heat duty load and reasonable temperature drop betweeneffects that renders best water production from the available wasteheat.

The MED system feed water is distributed onto the heat exchanger of thefirst effect in all of the trains. The second buffer fluid stream,heated in the 2^(nd) heat exchanger 13 b and the 4^(th) heat exchanger13 d, transfers some of its energy to the distributed feed water toevaporate a portion of the feed water. The produced vapor then condensesinto potable water in the heat exchanger of the second effect, and theheat of the condensation is used to evaporate more water in that effect.The brine from the first effect is then purged. At the second effect,the evaporated feed water goes on to power the third effect with theresulting brine being drained from the bottom of the effect. Thisprocess continues to the last effect within each train of each phasewith the corresponding produced vapor entering the condenser section tobe condensed by the incoming saline water acting as a coolant. Part ofthe pre-heated saline water is then sent to the various effects as feedwater. The saline water temperature can be between 25° C. and 35° C.(for example, about 28° C.), and the feed water temperature can bebetween 30° C. and 40° C. (for example, about 35° C.). The temperaturedrop from one effect to the next can be between 3° C. and 7° C. (forexample, 5° C.).

In some implementations, a steam booster unit is included in the MEDsystem to better exploit the waste heat stream to increase the freshwater yield. The steam booster unit includes an evaporator powered bythe outgoing waste heat source of the MED system. The vapor generatedfrom the steam booster unit is introduced into a suitable effect of theMED system. The inclusion of the steam booster unit in the MED systemcan increase the production rate to the extent allowed by thetemperature drop across the steam booster unit.

In some implementations, one or more flashing chambers can be includedin the MED system to improve the efficiency of the MED system, toextract more energy from the waste heat, and to utilize the extractedenergy to generate stream, thereby increasing fresh water production. Insuch implementations, the outlet source from the MED system goes on toheat the feed water via a liquid-liquid heat exchanger, which isslightly heated by the outlet brine stream from the last flashingchamber. The heated feed water goes through a series of flashingchambers. The vapor generated from each stage of the flashing is theninjected into an effect of the MED system for further boosting.

By identifying a best match between the waste heat load temperatureprofile and the number of effects used in each train, the quantity ofwater that can be generated using the MED system is optimized.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims.

The invention claimed is:
 1. A system comprising: a waste heat recoveryheat exchanger network comprising heat exchangers coupled to a a NaturalGas Liquid (NGL) fractionation plant, the NGL fractionation plantcomprising a propane dehydration section comprising a propane dehydratorcolumn and a de-propanizer section comprising a de-propanizerdistillation column, wherein the heat exchangers comprise: a first heatexchanger thermally coupled to the propane dehydration section to heat afirst buffer stream using heat carried by a propane de-hydration outletstream from the propane de-hydration section; and a second heatexchanger thermally coupled to the de-propanizer section to heat asecond buffer stream using heat carried by a de-propanizer overheadoutlet stream, wherein the first buffer stream is a first type of bufferfluid, and wherein the second buffer stream is a second type of bufferfluid different than the first type; and a first sub-system comprising apower turbine and heat exchangers, the first sub-system coupled to thewaste heat recovery heat exchanger network and configured to generatepower and sub-ambient cooling capacity using heat provided by the firstbuffer stream.
 2. The system of claim 1, further comprising a flowcontrol system connected to the heat exchanger network and the firstsub-system and comprising pumps, pipe, and valves to flow fluids betweenthe NGL fractionation plant, the heat exchanger network, and the firstsub-system, wherein the fluids comprise buffer fluid and NGLfractionation plant streams.
 3. The system of claim 1, comprising: afirst collection-header conduit to receive the first buffer streamdischarged from the first heat exchanger, wherein the firstcollection-header conduit to route the first type of buffer fluid to thefirst sub-system; and a second collection-header conduit to receive thesecond buffer stream discharged from the second heat exchanger.
 4. Thesystem of claim 1, wherein the NGL fractionation plant comprises abutane de-hydrator section comprising a butane dehydrator column and ade-butanizer section comprising a de-butanizer distillation column, andwherein the heat exchangers comprise: a third heat exchanger thermallycoupled to the butane de-hydrator section to heat a third buffer streamusing heat carried by a butane de-hydrator outlet stream; and a fourthheat exchanger thermally coupled to the de-butanizer section to heat afourth buffer stream using heat carried by a de-butanizer overheadoutlet stream.
 5. The system of claim 4, wherein the NGL fractionationplant comprises a de-pentanizer section comprising a de-pentanizerdistillation column, an Amine-Di-Iso-Propanol (ADIP) regenerationsection comprising an ADIP regenerator distillation column, a naturalgas (NG) de-colorizing section comprising NG decolorizerdistillation-column, a propane vapor recovery section comprising acompressor and a condenser heat exchanger, and a propane productrefrigeration section comprising a propane refrigeration compressor,wherein the heat exchangers comprise: a seventh heat exchanger thermallycoupled to the de-pentanizer section to heat a seventh buffer streamusing heat carried by a de-pentanizer overhead outlet stream from thede-pentanizer section; and an eighth heat exchanger thermally coupled tothe ADIP regeneration section to heat a eighth buffer stream using heatcarried by an ADIP regeneration section overhead outlet stream.
 6. Thesystem of claim 5, wherein the heat exchangers comprise: a ninth heatexchanger thermally coupled to the ADIP regeneration section, the ninthheat exchanger configured to heat a ninth buffer stream using heatcarried by an ADIP regeneration section bottoms outlet stream; a tenthheat exchanger thermally coupled to the natural gas de-colorizingsection, the tenth heat exchanger configured to heat a tenth bufferstream using heat carried by a natural gas de-colorizing sectionpre-flash drum overhead outlet stream; an eleventh heat exchangerthermally coupled to the natural gas de-colorizing section, the eleventhheat exchanger configured to heat an eleventh buffer stream using heatcarried by a natural gas de-colorizer overhead outlet stream; a twelfthheat exchanger thermally coupled to the propane vapor recovery section,the twelfth heat exchanger configured to heat a twelfth buffer streamusing heat carried by a propane vapor recovery compressor outlet stream;and a thirteenth heat exchanger thermally coupled to the propane productrefrigeration section, the thirteenth heat exchanger configured to heata thirteenth buffer stream using heat carried by a propane refrigerationcompressor outlet stream from the propane product refrigeration section.7. The system of claim 4, wherein the heat exchangers comprise: a fifthheat exchanger thermally coupled to the de-butanizer section, the fifthheat exchanger configured to heat a fifth buffer stream using heatcarried by a de-butanizer overhead outlet stream from the de-butanizersection; and a sixth heat exchanger thermally coupled to thede-butanizer section, the sixth heat exchanger configured to heat asixth buffer stream using heat carried by a de-butanizer bottoms outletstream from the de-butanizer section.
 8. The system of claim 4, whereinthe NGL fractionation plant comprises: a propane product sub-coolingsection comprising a main compressor and a propane condenserheat-exchanger; a butane product refrigeration section comprising abutane refrigeration compressor and a butane refrigeration condenserheat-exhanger; an ethane production section comprising an ethane dryercolumn; and a Reid Vapor Pressure (RVP) control section comprising a RVPdistillation column.
 9. The system of claim 8, wherein the heatexchangers comprise: a fourteenth heat exchanger thermally coupled tothe propane product sub-cooling, the fourteenth heat exchangerconfigured to heat a fourteenth buffer stream using heat carried by apropane main compressor outlet stream from the propane productsub-cooling section; a fifteenth heat exchanger thermally coupled to thebutane product refrigeration section, the fifteenth heat exchangerconfigured to heat a fifteenth buffer stream using heat carried by abutane refrigeration compressor outlet stream from the butane productrefrigeration section; a sixteenth heat exchanger thermally coupled tothe ethane production section, the sixteenth heat exchanger configuredto heat a sixteenth buffer stream using heat carried by an ethane dryeroutlet stream; and a seventeenth heat exchanger thermally coupled to theRVP control section, the seventeenth heat exchanger configured to heat aseventeenth buffer stream using heat carried by a RVP control columnoverhead outlet stream.
 10. The system of claim 4, wherein the thirdbuffer stream comprises the first type, and wherein the fourth bufferstream comprises the second type.
 11. The system of claim 1, wherein thefirst sub-system comprises a Goswami cycle system comprising the powerturbine and the heat exchangers.
 12. The system of claim 1, comprising asecond sub-system coupled to the waste heat recovery heat exchangernetwork, the second sub-system comprising train distillation effects togenerate potable water from brackish water by removing saline water fromthe brackish water.
 13. The system of claim 12, wherein the secondsub-system is configured to generate the potable water from brackishwater using heat provided by the second buffer stream.
 14. The system ofclaim 12, wherein the second sub-system comprises amulti-effect-distillation (MED) system comprising the train distillationeffects, the MED system configured to produce the potable water usingheat provided by the second buffer stream.
 15. The system of claim 14,wherein the MED system comprises a modified MED system comprising thetrain distillation effects.
 16. The system of claim 1, wherein the firsttype comprises oil and the second type comprises water.
 17. The systemof claim 1, further comprising: a first storage tank to store the firsttype of buffer fluid comprising the first buffer stream; and a secondstorage tank to store the second type of buffer fluid comprising thesecond buffer stream.
 18. The system of claim 17, wherein a flow controlsystem comprising pumps, pipes, and valves is configured to flow thefirst buffer stream or the second buffer stream or both from therespective storage tank to the waste heat recovery heat exchangernetwork.
 19. The system of claim 1, wherein the first sub-systemcomprises a modified Goswami cycle system configured to produce thepower and sub-ambient cooling capacity using heat carried by the firstbuffer stream.
 20. The system of claim 1, comprising; a first collectionheader conduit to receive the first type of buffer fluid discharged fromthe waste heat recovery heat exchanger network; and a second collectionheader conduit to receive the second type of buffer fluid dischargedfrom the waste heat recovery heat exchanger network.